The determination of hemoglobin and myoglogin residues as a parameter for testing heat exposure in back bacon.
(1/17330)
The use of an extraction of the heme pigments hemoglobin and myoglobin as a test for the heat exposure of back bacon was investigated by treating back bacon at varying temperatures of 50-70 degrees C and times of two to 180 minutes and observing the effect on the absorbance of heme pigment residue after nitrite oxidation. Absorbance at 409 nm was used in place of the more usual 540 nm to provide greater sensitivity in the detection of heme. A decrease in residual heme pigments was time-dependent, particularly at lower temperatures. In view of this factor and the complex nature of the heat exposure of a large block of back bacon, the application of this test would require a calibration of each process. Alternatively, limits to the amounts of heme pigment residue could be set. The heme pigment test is useful in its simplicity and overcomes difficulties associated with the coagulation and enzyme tests. (+info)
Fecal coliform elevated-temperature test: a physiological basis.
(2/17330)
The physiological basis of the Eijkman elevated-temperature test for differentiating fecal from nonfecal coliforms was investigated. Manometric studies indicated that the inhibitory effect upon growth and metabolism in a nonfecal coliform at 44.5 degrees C involved cellular components common to both aerobic and fermentative metabolism of lactose. Radioactive substrate incorporation experiments implicated cell membrane function as a principal focus for temperature sensitivity at 44.5 degrees C. A temperature increase from 35 to 44.5 degrees C drastically reduced the rates of [14C]glucose uptake in nonfecal coliforms, whereas those of fecal coliforms were essentially unchanged. In addition, relatively low levels of nonfecal coliform beta-galactosidase activity coupled with thermal inactivation of this enzyme at a comparatively low temperature may also inhibit growth and metabolism of nonfecal coliforms at the elevated temperature. (+info)
A hyperstable collagen mimic.
(3/17330)
BACKGROUND: Collagen is the most abundant protein in animals. Each polypeptide chain of collagen is composed of repeats of the sequence: Gly-X-Y, where X and Y are often L-proline (Pro) and 4(R)-hydroxy-L-proline (Hyp) residues, respectively. These chains are wound into tight triple helices of great stability. The hydroxyl group of Hyp residues contributes much to this conformational stability. The existing paradigm is that this stability arises from interstrand hydrogen bonds mediated by bridging water molecules. This model was tested using chemical synthesis to replace Hyp residues with 4(R)-fluoro-L-proline (Flp) residues. The fluorine atom in Flp residues does not form hydrogen bonds but does elicit strong inductive effects. RESULTS: Replacing the Hyp residues in collagen with Flp residues greatly increases triple-helical stability. The free energy contributed by the fluorine atom in Flp residues is twice that of the hydroxyl group in Hyp residues. The stability of the Flp-containing triple helix far exceeds that of any untemplated collagen mimic of similar size. CONCLUSIONS: Bridging water molecules contribute little to collagen stability. Rather, collagen stability relies on previously unappreciated inductive effects. Collagen mimics containing fluorine or other appropriate electron-withdrawing substituents could be the basis of new biomaterials for restorative therapies. (+info)
Determination of pyrolysis products of smoked methamphetamine mixed with tobacco by tandem mass spectrometry.
(4/17330)
This study examines the pyrolysis products of smoked methamphetamine mixed with tobacco that was trapped with a C8 adsorbent cartridge and then detected by gas chromatography-tandem mass spectrometry. According to the results, the mainstream smoke contains 2-methylpropyl-benzene, 2-chloropropyl-benzene, 2,3-dihydro-3,5-dihydroxy-6-methyl-4H-pyran-4-one, 3-ethyl-phenol, methamphetamine, dimethylamphetamine, hydroquinone, 3-methyl-5-(1-methylethyl)-methylcarbamate phenol, N-methyl-N-(2-phenylethyl)-acetamide, 4-(3-hydroxy-1-butenyl)-3,5,5-trimethyl-2-cyclohexene-1-one, propanoic acid, N-acetylmethamphetamine, phenyl ester, and furfurylmethylamphetamine. In addition, the compounds in sidestream smoke are 2-propenyl benzene, phenylacetone, methamphetamine, dimethylamphetamine, benzyl methyl ketoxime, 3,4-dihydro-2-naphthalenone, N-folmyamphetamine, N-acetylamphetamine, bibenzyl, N-folmylmethamphetamine, N-acetylmethamphetamine, N-propionymethamphetamine, and furfurylmethylamphetamine. Moreover, the presence of methamphetamine promotes the oxidation of the tobacco components. (+info)
Identification and quantification of cocaine N-oxide: a thermally labile metabolite of cocaine.
(5/17330)
In this article, we report the identification and quantitation of cocaine N-oxide (CNO), a thermally labile oxidative metabolite, from both animal and human samples. The concentration of CNO is similar to the concentrations of cocaine in the samples analyzed. The technique used for the determination of CNO in this study is liquid chromatography-electrospray ionization mass spectrometry, which is necessary because CNO is converted to cocaine upon heating. This includes simple heating of aqueous solutions to temperatures in excess of 100 degrees C and analysis by gas chromatography-mass spectrometry (GC-MS), in which CNO is converted to cocaine in the injection port. The thermal conversion of CNO to cocaine is estimated to cause an over-reporting of cocaine levels by 10-20% when using GC-MS. (+info)
Adenoviral gene transfer into the normal and injured spinal cord: enhanced transgene stability by combined administration of temperature-sensitive virus and transient immune blockade.
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This study characterized gene transfer into both normal and injured adult rat dorsal spinal cord using first (E1-/E3-) or second (E1-/E2A125/E3-, temperature-sensitive; ts) generation of replication-defective adenoviral (Ad) vectors. A novel immunosuppressive regimen aimed at blocking CD4/CD45 lymphocytic receptors was tested for improving transgene persistence. In addition, the effect of gene transfer on nociception was also evaluated. Seven days after treatment, numerous LacZ-positive cells were observed after transfection with either viral vector. By 21 days after transfection, beta-galactosidase staining was reduced and suggestive of ongoing cytopathology in both Ad-treated groups, despite the fact that the immunogenicity of LacZ/Adts appeared less when compared with that elicited by the LacZ/Ad vector. In contrast, immunosuppressed animals showed a significant (P < or = 0.05) increase in the number of LacZ-positive cells not displaying cytopathology. In these animals, a concomitant reduction in numbers of macrophages/microglia and CD4 and CD8 lymphocytes was observed. Only animals that received LacZ/Adts and immunosuppression showed transgene expression after 60 days. Similar results were observed in animals in which the L4-L5 dorsal roots were lesioned before transfection. Gene transfer into the dorsal spinal cord did not affect nociception, independent of the adenovirus vector. These results indicate that immune blockade of the CD4/CD45 lymphocytic receptors enhanced transgene stability in adult animals with normal or injured spinal cords and that persistent transgene expression in the spinal cord does not interfere with normal neural function. (+info)
Role of DnaK in in vitro and in vivo expression of virulence factors of Vibrio cholerae.
(7/17330)
The dnaK gene of Vibrio cholerae was cloned, sequenced, and used to construct a dnaK insertion mutant which was then used to examine the role of DnaK in expression of the major virulence factors of this important human pathogen. The central regulator of several virulence genes of V. cholerae is ToxR, a transmembrane DNA binding protein. The V. cholerae dnaK mutant grown in standard laboratory medium exhibited phenotypes characteristic of cells deficient in ToxR activity. Using Northern blot analysis and toxR transcriptional fusions, we demonstrated a reduction in expression of the toxR gene in the dnaK mutant strain together with a concomitant increase in expression of a htpG-like heat shock gene that is located immediately upstream and is divergently transcribed from toxR. This may be due to increased heat shock induction in the dnaK mutant. In vivo, however, although expression from heat shock promoters in the dnaK mutant was similar to that observed in vitro, expression of both toxR and htpG was comparable to that by the parental strain. In both strains, in vivo expression of toxR was significantly higher than that observed in vitro, but no reciprocal decrease in htpG expression was observed. These results suggest that the modulation of toxR expression in vivo may be different from that observed in vitro. (+info)
Cloning and expression of the dnaK gene of Campylobacter jejuni and antigenicity of heat shock protein 70.
(8/17330)
Campylobacter jejuni is a leading cause of infectious diarrhea throughout the world. In addition, there is growing evidence that Guillain-Barre syndrome, an inflammatory demyelinating disease of the peripheral nervous system, is frequently preceded by C. jejuni infection. In the present study, the hrcA-grpE-dnaK gene cluster of C. jejuni was cloned and sequenced. The dnaK gene consists of an open reading frame of 1,869 bp and encodes a protein with a high degree of homology to other bacterial 70-kDa heat shock proteins (HSPs). The overall percentages of identity to the HSP70 proteins of Helicobacter pylori, Borrelia burgdorferi, Chlamydia trachomatis, and Bacillus subtilis were calculated to be 78.1, 60.5, 57.2, and 53. 8%, respectively. Regions similar to the Escherichia coli sigma70 promoter consensus sequence and to a cis-acting regulatory element (CIRCE) are located upstream of the hrcA gene. Following heat shock, a rapid increase of dnaK mRNA was detectable, which reached its maximum after 20 to 30 min. A 6-His-tagged recombinant DnaK protein (rCjDnaK-His) was generated in E. coli, after cloning of the dnaK coding region into pET-22b(+), and purified by affinity and gel filtration chromatography. Antibody responses to rCjDnaK-His were significantly elevated, compared to those of healthy individuals, in about one-third of the serum specimens obtained from C. jejuni enteritis patients. (+info)